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In the News: Oracle RAC 10g on Linux x86
Several clients have asked about the major components of Oracle RAC 10g and using it in combination with Linux servers. EEI is well versed in the architecture and is ready and prepared as you bring your company forward into that environment. Following is a quick overview of the major components.
Shared Disk Storage
Oracle RAC relies on a shared disk architecture. The database files, online redo logs, and control files for the database must be accessible to each node in the cluster. The shared disks also store the Oracle Cluster Registry and Voting Disk. There are a variety of ways to configure shared storage including direct attached disks (typically SCSI over copper or fiber), Storage Area Networks (SAN), and Network Attached Storage (NAS).
Private Network
Each cluster node is connected to all other nodes via a private high-speed network, also known as the cluster interconnect or high-speed interconnect (HSI). This network is used by Oracle's Cache Fusion technology to effectively combine the physical memory (RAM) in each host into a single cache. Oracle Cache Fusion allows data stored in the cache of one Oracle instance to be accessed by any other instance by transferring it across the private network. It also preserves data integrity and cache coherency by transmitting locking and other synchronization information across cluster nodes.
The private network is typically built with Gigabit Ethernet, but for high-volume environments, many vendors offer proprietary low-latency, high-bandwidth solutions specifically designed for Oracle RAC. Linux also offers a means of bonding multiple physical NICs into a single virtual NIC to provide increased bandwidth and availability.
Public Network
To maintain high availability, each cluster node is assigned a virtual IP address (VIP). In the event of host failure, the failed node's IP address can be reassigned to a surviving node to allow applications to continue accessing the database through the same IP address.
Oracle Cluster Ready Services
Oracle RAC 10g introduced Oracle Cluster Ready Services (CRS), a platform-independent set of system services for cluster environments. In prior releases of RAC and Oracle Parallel Server, Oracle relied on vendor-supplied cluster management software to provide these services. Although CRS works in concert with vendor-supplied clusterware, the only required component for Oracle RAC 10g is CRS. Indeed, CRS must be installed prior to installing RAC.
CRS maintains two files: the Oracle Cluster Registry (OCR) and the Voting Disk. The OCR and the Voting Disk must reside on shared disks as either raw partitions or files in a cluster filesystem.
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